MPS-1-IN-1 is a selective, potent small molecule inhibitor of Mps1. Mps1, a dual-specificity kinase, is required for the proper functioning of the spindle assembly checkpoint and for the maintenance of chromosomal stability. Mps1 inhibition increases the frequency of multipolar mitoses. Lastly, Mps1 inhibitor treatment resulted in a decrease in cancer cell viability. [1]